1. Field of the Invention
The present invention relates to a method for preparing a CIS (Cu—In—Se) compound and a thin film, and a solar cell having the CIS compound thin film.
2. Description of the Related Art
A CIS (Cu—In—Se) compound, representatively CuInSe2, is used for an absorption layer of a solar cell. To make an absorption layer using CuInSe2, there are generally used a method for depositing CuInSe2 on a substrate in a vacuum and a method for coating CuInSe2 precursor in non-vacuum and then thermally treating it at a high temperature. Among them, the vacuum deposition is advantageous in making a high-efficient absorption layer, but it shows deteriorated uniformity when making a large-sized absorption layer and also needs an expensive equipment. Meanwhile, the method of coating precursor materials and then thermally treating them at a high temperature allows one to make a large-sized absorption layer uniformly, but it shows low efficiency of the absorption layer.
Among various absorption layer making methods using precursor materials, a method of coating paste of a metal oxide mixture on a substrate and then thermally treating them to make an absorption layer seems to be most suitable for practical use in mass production. This method may allow one to make uniform absorption layers at a low cost. However, since metal oxide precursor is very stable chemically and thermally, it is difficult to obtain large crystals in a final absorption layer, which results in lowered efficiency.
In addition, Japanese Laid-open Patent Publication No. 2001-053314 discloses a method for forming a thin film by spraying a dispersion solution containing Cu and Se powder and organic metal salt of In on a conductive substrate and then thermally treating it under a non-oxidizing environment, but this method needs more improvement in its productivity.
Also, Japanese Patent No. 3589380 discloses a technique for forming CuInSe2 by soaking a substrate into a solution in which a salt of an element in the 3B group of the periodic table (e.g., InCI3), an organic material containing an element in the 6B group (e.g., CH3CSeNH2), and an acid (e.g., HCl), but it needs more improvement in use of CuInSe2 itself during reaction and suffers from a generally low reaction yield.
In addition, U.S. Pat. No. 6,127,202 discloses a method for making CIGS (Cu—In—Ga—Se) by reacting a mixture of metal oxide nano particles under reduction environment and selenium gas environment, and U.S. Pat. No. 6,268,014 discloses a method for reacting a mixture of metal oxide and non-oxide particles under reduction environment and selenium environment.